1. Field of the Invention
This invention relates to a variable color display device having display area and background area.
2. Description of the Prior Art
A driving circuit for light emitting diodes, described in U.S. Pat. No. 3,740,570, issued on Jun. 19, 1973 to George R. Kaelin et al., utilizes special light emitting diodes that emit light of different colors in response to different currents.
An electronic display having segments wherein each segment is capable of selectively illuminating two colors is disclosed in U.S. Pat. No. 4,488,149 issued on Dec. 11, 1984 to William A. Givens, Jr. Two AND gates are provided for biasing, in each display segment, either a first light emitting diode, for emitting a first color, or a second light emitting diode, for emitting a second color. It is not contemplated to illuminate both light emitting diodes in each segment simultaneously for blending the colors.
A multi-colour LED display for seven segment figures is disclosed in German Patent No. 3,009,416 issued on Sep. 17, 1981 to Klaus Gillessen. The LED circuit consists of seven group of diodes, each group made up of two diodes, one red and one green. The cathodes of all red diodes are terminated in a common connection, and the green ones likewise, the anodes of each pair of diodes being common for that pair. Two transistors connected in cascade are utilized for activating either all green LEDs, or all red LEDs, but not both simultaneously. When a low level signal is applied to the base of the first transistor, the first transistor is blocked, and the second transistor is turned ON to illuminate the second set of the diodes. When a high level signal is applied to the input of the first transistor, the first transistor is turned ON, while the second transistor is blocked, whereby the first set of the diodes is illuminated. Since the first transistor cannot be simultaneously turned ON and OFF, it would be impossible to illuminate the two sets of the diodes simultaneously. In another embodiment is shown a multi-colour LED display utilizing three sets of LEDs: red, green, and blue, which are respectively commonly connected and may be activated by manual switches. It is not contemplated that the three sets of LEDs be activated in selective combinations to blend the colors.
A digital electrooptical display with anti-parallel light emitting diodes is disclosed in East German Patent No. 220,844 issued on Apr. 10, 1985 to Thomas Hoffman et al. Two light emitting diodes for emitting light of different colors are connected in each segment back-to-back. Since the light emitting diodes are connected to conduct currents in opposite directions, it would be impossible to illuminate them simultaneously, because the opposite currents would cancel.
A method and apparatus for independent color control of alphanumeric display and background therefor are disclosed in U.S. Pat. No. 3,911,418, issued on Oct. 7, 1975 to Minoru Takeda. In order to exhibit a character in a desired color, the code of the character and its color code are entered from a keyboard. A color code for the background area is then entered from the keyboard, independently of the color code for the displayed character. All entered codes are then encoded into a composite train of pulses, which are then separated, decoded, and used for exhibiting on a cathode ray tube device the desired character in the desired color, and for controlling color of its background.
The prior art does not contemplate a variable color light emitting diode display device having display area and background area, in which the display light emitting diodes are coupled to, and controlled by, display buses, and the background light emitting diodes are coupled to, and controlled by, background buses.